From	Jonathan T. Overpeck	Date	Tue, 19 Sep 2006 11:37:49 -0600
To	Gabi Hegerl
CC	Keith Briffa, Eystein Jansen
Subject	Re: cheers!
Hi Gabi - we do loose quite a bit (e.g., boreholes and other proxies) back beyond 500, so that's why we drew the "very likely" line there. But, we did stay as strong as the TAR back 1300, so that was our compromise on certainty. I believe the forcing series also start to get more uncertain pretty fast back beyond even 400 years ago, but I'm pretty impressed with the match between simulated and observed NH climate back ca. 700 years (e.g., our Figs 6.13 and 6.14). Thus, I bet you are right that we know back to 700 pretty well, but not well enough to go with "very likely" in the all important chap 6 bullet. Not sure this helps, but we do need to pay attention as we do the SPM to get the right balance. I'll cc to Keith in case he wants to chime in, which would be appreciated. thanks, peck >p.s. hope you are all recovered etc! >I have one chapter question: We were waffling back and forth if we >SHOULD go with the chapter 6 >assessment on the last 500 being better reconstructed than say last >700, but in the end, we stuck with >last 700 because some results rely on using a long timehorizon to >separate like ghg and solar signals. >To say that very likely a substantial fraction of the variance on >those records is externally forced (nother >words, detectable external signals in reconstructions). >Does this seem ok to you? In the SPM session we had some waffling >about 5 vs 7 centuries. > >Gabi > >Jonathan Overpeck wrote: -- Jonathan T. Overpeck Director, Institute for the Study of Planet Earth Professor, Department of Geosciences Professor, Department of Atmospheric Sciences Mail and Fedex Address: Institute for the Study of Planet Earth 715 N. Park Ave. 2nd Floor University of Arizona Tucson, AZ 85721 direct tel: +1 520 622-9065 fax: +1 520 792-8795 http://www.geo.arizona.edu/ http://www.ispe.arizona.edu/